Multiple spool power pack unit

ABSTRACT

A power pack for converting gas pressure into rectilinear movement of a drive shaft. The power pack is actuated by unseating the primary spool of a spool mechanism having a primary spool and a secondary spool releasing a volume of pressurized gas and thereby driving a shaft adapted to be associated with a mechanism requiring an input of rectilinear movement. Differential pressures cause the spool mechanism to be reseated, thus allowing the drive shaft, biased toward the spool, to return to its rest position. The operation of the power unit depends upon the formation of pressure-tight chambers by the spool mechanism and associated O-rings and the sealing ability of the primary spool to slidably seal the flow of pressurized gas.

United States Patent [191 Noiles et al.

[ 1 Sept. 16, 1975 MULTIPLE SPOOL POWER PACK UNIT [73] Assignee: UnitedStates Surgical Corporation,

Baltimore, Md.

[22] Filed: Sept. 29, 1972 21 Appl. No.: 293,469

3,583,426 6/1971 Feres 251/174 X 3,613,507 10/1971 Smith, Jr 91/433 XFOREIGN PATENTS OR APPLICATIONS 1,257,410 2/1961 France 91/465 1,002,0918/1965 United Kingdom 137/59614 Primary Examinerlrwin C. Cohen Attorney,Agent, or FirmFleit & Jacobson 57 ABSTRACT A power pack for convertinggas pressure into rectilinear movement of a drive shaft. The power packis actuated by unseating the primary spool of a spool mechanism having aprimary spool and a secondary spool releasing a volume of pressurizedgas and thereby driving a shaft adapted to be associated with amechanism requiring an input of rectilinear movement. Differentialpressures cause the spool mechanism to be reseated, thus allowing thedrive shaft, biased toward the spool, to return to its rest position.The operation of the power unit depends upon the formation ofpressure-tight chambers by the spool mechanism and associated O-ringsand the sealing ability of the primary spool to slidably seal the flowof pressurized gas.

14 Claims, 14 Drawing Figures mamas E 1 :915 9 sum 2 OF 3 052 {6MULTIPLE SPOOL POWER PACK UNIT BACKGROUND OF THE INVENTION The generalconcept of a gas powered driving unit as disclosed by the presentapplication is not new. See for example, U.S. Pat. Nos. 3,613,507,issued Oct. 19, 1971; 3,618,842, issued Nov. 9, 1971 and 3,643,851,issued Feb. 22, 1972, all of which are assigned to the present Assignee.Additional prior art of interest can be found in the art cited by thePatent Office during the prosecution of the above-identified patents.

The power unit described in each of the above-noted patents functionscapably. However, each of the abovementioned power units suffers fromcertain disadvantages. For example, the power unit described in US. Pat.No. 3,613,507 has a small seal area which with repeated seatings maybecome damaged thus preventing good contact between mating surfaces.Consequently, the sealing area increases because of plastic deformationand can ultimately create an area large enough for pressure forces toexceed spring forces in the other direction and hence the power unitcould fail due to leakage.

In the power unit described in US. Pat. No. 3,618,842, the pressurechambers are defined by a se ries of O-rings which after long periods ofwear may result in leakage between one chamber and the next.

In the third US. Pat, No. 3,643,851, the gas chamber is defined by aplurality of sliding diaphragms. These diaphragms were found to besomewhat Weak and, in time, often developed leaks.

It is towards the elimination of the above-noted disadvantages and thesimplification of known power pack units that the present invention isdirected.

SUMMARY OF THE INVENTION The present invention relates to a power packcapable of converting gas pressure into rectilinear movement, using aminimum amount of pressurized gas and with a minimum of moving parts.Pressurized gas is fed into the inventive power pack and when the powerpack is idle the spool mechanism of the power pack is sealed off fromthe gas pressure. The two-part movable spool mechanism is maintained inconstant contact with the gas pressure through the action of a pilotvalve which has a gas port through its center. The contact between therear of the spool mechanism and the pilot valve seals off thepressurized gas with the flat surface of the outer end of the valveabutting the flat surface of the inlet valve body allowing the pilotvalve to have random orientation contact without damaging the seal.

The power pack of the present invention is fired when the driving pistonand integral drive shaft are moved against the force of the pistonreturn biasing spring. This movement allows the spool mechanism tobecome unsealed from the pilot valve and held in its unseated positionthrough the action of pressurized gas acting upon the surfaces of thespool mechanism. When the spool is unseated the source of pressurizedgas acts upon the piston integral with the drive shaft. The drive shaftis then driven by the pressurized gas through a firing cycle.

During the return movement of the piston, the force on the face of thespool mechanism remote from the gas port becomes greater than the forceon the face of the spool mechanism adjacent the gas port, so that thespool mechanism is driven toward the gas port seating it against thepilot valve to seal the source of gas pressure. When the drive shaft isreturned by its biasing spring, the gas in the piston chamber isexhausted, and the piston is brought into contact with the spoolmechanism. At this time the power unit is ready for another drive cycle.

The operation of the inventive power pack is dependent upon the selfenergizing seal of the pilot valve, and the two-part spool mechanismwith its sealing O-rings. Furthermore, the total area of the pilot valvesealing surface is such that it cannot become enlarged enough to misfireas there is always a sealing contact between the flat surfaces of thevalve lip and the flat end surface primary spool projecting tip allowinga random orientation contact of the pilot valve body without damagingthe seal. In addition, the unit provides for a cushioning effect on itsvarious component parts. The rearward thrust of the spool mechanismcausing contact with the pilot valve body is cushioned by twoindependent forces. The first force, and the lesser of the two,originates in the pilot valve biasing spring which at all times urgesthe pilot valve toward the spool mechanism and thus absorbs the contactforce when the spool mechanism strikes the pilot valve body. The secondforce originates in the pressure of the inlet acting on the netcross-sectional areaof the pilot valve body.

Also, the forward unit of the drive shaft is against the biasing springwhich at all times urges the drive shaft and integral piston toward thespool mechanism.

As constructed, the power pack forming the present invention has twomajor moving elements comprising a spool mechanism having two movableparts and a movable pilot valve body. The life of the power pack issubstantial because of the minimal amount of wear on the apparatus sothat it has great reliability for long periods of use. Furthermore, theapparatus also provides a means of transforming pressure forces intorectilinear motion in an efficient and reliable manner.

By utilizing the present invention, whose parts have tolerances that arerelatively loose, the need for high precision machinery is eliminated asthe manufacturing tolerances do not have to be so precise. Even withoutclose tolerance of the parts as compared with similar units of the priorart, substantial thrust is able to be developed in the drive shaft withthe effect that the moving parts are returned to their prefiringpositions by combining the effects of the gas pressure and a singlebiasing spring.

Other features and advantages of the invention will be apparent from thefollowing description of the embodiments of the invention as shown inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross sectionthrough a power pack constructed in accordance with the teachings of thepresent invention.

FIG. 2 is a cross section view of the inlet valve body shown in FIG. Iin relation to the piston.

FIG. 3 is the right end elevation view of the inlet valve body of FIG.2.

FIG. 4 is a cross section view of the secondary spool body shown in FIG.1.

FIG. 5 is the left end elevation view of the secondary spool body ofFIG. 4.

FIG. 6 is a cross section view of the primary spool body shown in FIG.1.

FIG. 7 is the left end elevation view of the primary spool body shown inFIG. 6.

FIG. 8 is a cross section view of the pilot plug housing shown in FIG.1.

FIG. 9 is plan view of the pilot plug housing shown in FIG. 8.

FIG. 10 is the right end elevation view of the pilot plug housing ofFIG. 8.

FIG. 11 is an enlarged cross section view of the pilot valve body shownin FIG. 1.

FIG. 12 is the left end elevation view of the pilot valve body of FIG.11.

FIG. 13 is a side view of the filter shown in FIG. 1.

FIG. 14 is a plan view of the filter illustrated in FIG. 13.

DETAILED DESCRIPTION OF THE DRAWINGS:

As shown in FIGS. 114 the inventive power pack generally discloses anouter casing 22 in which is mounted an inlet valve body 30 containing aprimary spool body 62, a secondary spool body 79, a pilot housing 46 anda pilot valve body 54. A drive shaft 24 is slidably mounted in the outercasing with the foremost end of the drive shaft (not shown) being theoutput side of the power pack and serving to operate any devicedepending upon a rectilinear motion input for its performance.

The rearwardmost end of the drive shaft takes the form of a piston 26slidably mounted in a piston chamber 28 defined by an inner casingmember 29. The piston 26 is held in position by a piston return Springwhich exerts a force on the piston 26 of approximately 11 to 12 pounds.The inner casing member 29 is mounted in a fixed position within theouter casing 22.

Mounted in the outer casing 22 adjacent the inner casing member 29 is aninlet valve body 30. The inlet valve body 30 as shown in FIGS. 2 and 3defines two centrally located interconnected chambers; a stepped spoolchamber 58 and a pilot housing chamber 45 which are interconnected byport 56 and vents 47. The stepped spool chamber 58 preferably comprisestwo sections or steps each of which has a different diameter, the largersection 57 being of sufficient diameter to hold the primary spool body62, the other 59 being of sufficient diameter to hold the second spoolbody 79. The outer surface of the inlet valve body 30 defines aplurality of annular channels 36, 94, 124 and 126. An exhaust port 92 iscut through the inlet valve body 30 to connect chamber section 57 withan annular exhaust channel or ring 94. The inlet valve body also definesa filter chamber 37 which is connected to the pilot housing chamber 45by inlet passageway 42.

A stainless steel capillary tubing 32 leads from the gas pressure source(not shown) through the outer casing 22 into the gas feed channel 36 ofthe inlet valve body so that the source of pressurized gas can operatethe working mechanism of the power pack 20. The pressurized gas enterschannel 36 from the capillary tubing 32 at 34 and travels into the inletvalve body filter chamber 37. The gas is filtered by filter 38 on itsway into passageway 42 which communicates with annulus 48 in housingchamber 45. The annulus 48 is defined by the inlet valve body 30, theouter surface of the pilot housing 46 and O-ring 50 seated inside thehousing chamber 45 and abutting the housing body shoulders 43. The pilothousing 46 as shown in FIGS. 1, 8 and 9, is preferably threaded so thatit can be screwed into the inlet valve body 30 by means of a driv ingslot 110. A blind hole is drilled in the pilot housing to form the pilotvalve chamber 44. The blind end of chamber 44 is used as a spring seatfor the pilot valve biasing spring 108. The chamber 44 is preferablystepped to allow clearance for shoulder 103 on pilot valve body 54. Afilter chamber 53 holds filter 55. The filter chamber 53 communicateswith the pilot chamber 44 by means of a port 57 cut through the pilothousing 46. Filter chamber 53 also communicates with feed chamber 48 bypassageway 51. A pilot valve body 54 is slidably fitted into pilothousing chamber 44 in a gas tight relationship by means of O-ring 100.

The pilot valve body 54 as shown in FIGS. 11 and 12 is constructed witha bore 96 which allows gas entering port 56 to flow through it. Anannular channel 98 is cut into the valve body to hold O-ring so that theO- ring 100 will form a gas-tight seal between the wall of chamber 44and the outer surface of the valve body 54. The biasing spring 108 hasone end seated in the blind end of chamber 44 and the other endsurrounding the pilot valve body at the spring rest 99 where it abutsagainst the pilot valve body to urge the pilot valve body away from theblind end of chamber 44 toward the spool mechanism. The other end of thepilot valve body which performs the sealing functions comprises ashoulder portion 103, the front surface of which has a flat surface tocontact the flat surface of the inlet valve body contact area 60.Counterbore 41 in the pilot housing provides clearance for shoulder 103.The forward edge of the pilot valve body slopes upward from the flatsurface of shoulder 103 to form an annular ring 102 which has a flatsealing surface surrounding the bore 97. Thus there is formed on theforward edge of the pilot valve body a geometric surface which does nothave to hit the same point repeatedly and therefore never spreads theseal area. When the valve is closed, ring 102 abuts fiat surface 68 onprimary spool 62. Inlet gas pressure works on an area created bydiameter of body 54 less diameter of bore 96 to hold the valve closed.The same pressure also works on the much smaller area of ring 102 lessthat of bore 96. The net effect is that the inlet gas pressure holds thevalve closed providing that the bias of spring 25 is strong enough toprevent the gas pressure on body 54 from moving primary spool 62.

Adjacent the pilot valve chamber 44 is spool port 56 cut through theinlet valve body contact area 60. The spool port 56 allows thepressurzed gas passing though the pilot valve bore 96 to pass into thestepped spool chamber 58. A plurality of vents 47 are also cut throughthe inlet valve body contact area 60 substantially parallel to the spoolport 56 and located approximately adjacent the flat forward surface ofthe pilot valve body shoulder 103. As the pilot valve body 54 movesforward its shoulder 103 hits the contact area 60 thus stopping thepilot body and keeping it in position until its return.

Mounted in the inlet valve spool chamber 58 is a primary spool body 62as shown in FIGS. 6 and 7 having a centrally positioned bore 64connected to the spool chamber by a feed port 66. The feed port 66serves to admit gas to the working surface of piston 26 from the pilotvalve bore 96 against the piston head 26. The rearward end of primaryspool body 62 forms a projecting tip 68 which is adapted to seat againstthe pilot valve body 54 forming a gas-tight seal and preventing gas fromentering into spool chamber 58, except when the unit is actuated. Theend of projecting tip 68 has a flat surface and a greater total areathan the area of the pilot valve lip 102. In addition, sealing contactis always between flat surfaces, so that there can be random orientationcontact without damaging the seal. The primary spool body 62 alsodefines an annular rib 70 having a shoulder 72 upon which is seated afree floating O-ring 74. The annular rib 70 preferably fits within bore80 of the secondary spool body 79 to guide the primary spool body alongthe inner surface 81 of the secondary spool body. The other end of theprimary spool body 62 defines a forward head 63 which is adapted toengage piston head 26. The outer circumference of the forward headterminates in an outer rib 76 having a shoulder 77 cut therein. Anescape port 75 is cut through the outer rib 76 so that gases exhaustedby the returning piston 26 escape through port 75 in the forward head 63into chamber 83 fonned by the primary spool body and secondary spoolbody in the spool chamber 58. The shoulder 77 is adapted to form achannel or seat in cooperation with the secondary spool to hold O-ring78. The shoulder 77 in cooperation with the secondary spool body placesthe O-ring 78 under compression so that the O-ring will expand towardthe piston 26 thus forcing the primary spool body 62 forward when thecompressive forces of the piston 26 on the forward head 63 of theprimary spool body are lessened.

As shown in FIGS. 1, 4 and 5, a secondary spool body 79 having a bore 80therethrough surrounds the annular rib 70 of the primary spool body 62to form the O- ring seat for O-ring 74. The rear of the secondary spoolbody 79 has a plurality of radial slots 82 cut from the outer surface ofthe spool body 79 to the bore 80 so that when the rear end wall of thesecondary spool body 79 engages the rear wall of body chamber section59, the annulus 87 is in communication with bore 80. The outer surfaceof the spool body 79 is stepped outward from the end wall to define ashoulder 84 and a seat 85 which are adapted to seat and hold a freefloating O-ring 86. The forward portion of the secondary spool body 79takes the form of an annular ring 88. The ring 88 has an annular notch89 cut into it to form the other part of the seat for O-ring 78, incooperation with the abutting shoulder 77 of the primary spool body. Itshould be noted that the abutting shoulder 77 of the primary spool bodydoes not form a level seat for O- ring 78 when it abuts notch 89.Exhaust channels 90 are provided through the ring 88 so that the exhaustgas moved by the return of the piston 26 can pass from exhaust area 87through primary spool exhaust port 75 into chamber 83. From chamber 83the gas passes through channels 90 into exit port 92 and the exhaustring 94 of the inlet valve body. The gas is carried by the exhaust ring94 to exhaust conduit 95 in the outer body 22 where the gases are ventedto the atmosphere.

In the unit, a washer 116 is preferably placed under the head of theplug housing in contact the-inlet valve body surrounding O-ring 118 toprovide a suitable gas seal. In addition, inlet valve body O-rings 120and 122 are placed in respective channels 124 and 126 of the inlet valvebody so that the inlet gas is sealed between these O-rings.

The unit is maintained in its readiness condition by means of a coilspring 25 acting on the piston 26, which spring exerts a force greaterthan that developed by the spring 108, plus the gas pressure acting onthe area of the diameter of the body 54. A trigger notch (not shown) islocated in an output shaft 24 integral with the piston 26. Uponactivation of a trigger 27 the output shaft 24 and its integral piston26 move in the direction of arrow A. Then, under the force of spring 108and that developed by the pressurized gas, the pilot valve body 54, thespool bodies 62, 79 and the piston 26 move in unison until the frontface of the pilot valve body 54 abuts surface 60 of the inlet valve body30.

The piston is pulled further forward by the trigger to allow the forceof the gas pressure passing through bore 97 of the pilot valve body toact against the rearward surface of the primary spool 62 in combinationwith the resilient action of O-ring 78 against shoulder 77 to move theprimary spool body 62 until the driving head 63 of the primary spoolbody abuts against the piston chamber walls 29 creating a sealtherewith. The pilot valve body 54 cannot follow the primary spool body62 because port 56 is smaller than the shoulder 103 of the pilot valvebody. Thus, after projecting tip 102 of the pilot valve body 54 projectsinto port 56 the pilot valve body shoulders 103 strike the flat surfaceof the contact area 60 stopping movement of the pilot valve body.Pressurized gas pours through the bore 96 of the pilot valve body intothe spool chamber 58 to seat O-ring 74 against shoulder 72, guide ringand the inner surface 81 of the secondary spool body to form a gas-tightseal. As the primary spool body 62 is moved forward, gas continues topass through orifice 66 in the primary spool body 62 into the lesserpressure of chamber 64 of the primary spool to drive piston 26 forward.At the same time that pressurized gas begins to enter the spool chamber58 the gas travels through radial slots 82 of the secondary spool bodycausing the O-ring 86 to seat against the shoulder 84, end wall and theinner surface of the spool chamber 58 to form a gas-tight seal. When theprimary spool body 62 has traveled forward, the gas pressure pushes thesecondary spool body forward until its forward edge contacts shoulder 77of the primary spool body. The contact between the primary spoolshoulder 77 and the secondary spool seats O-ring 78 in a state ofcompression so that it can act on the primary spool body when the piston26 is removed from contact with the primary spool body.

When the piston chamber 59 is filled with gas, the pressure ratiosbecome such that the spool mechanism is returned rearward to its initialposition. As a greater area of pressure is formed on the face of theprimary spool body on the piston side as opposed to the lesser area ofpressure formed on the rear surfaces of the primary spool body andsecondary spool body, the greater force pushes the primary spool bodyrearward by carrying both spool bodies back until the flat end surfaceof the tip projection 68 is seated against the pilot spool body lip 102to seal the pilot valve body bore 96 and close the valve. As the spoolmechanism is returned, gas pressure acting on the diameter of the pilotvalve body 54 serves along with spring 108 to absorb the effect of thetip projection 68 striking the lip 102. This cushioned action eliminatesimpact on lip 102 so that the surfaces will continue to form a gas-tightseal after repeated use.

Functionally, the pilot valve works fully well without spring 108. Thepurpose of spring 108 is to insure that the valve is in the closedposition when initially pressurized. The force due to pressure acting onpilot valve body is several times greater than that of spring 108. Forexample, in the preferred embodiment the pressure force on the spring108 is less than one pound with the pressure force acting on the pilotvalve body being equal to to 6 pounds.

A gas exhaust is provided in the apparatus as the pressurized gasreturned by the returning piston head 26 acted on by spring 25, isforced into the annular channel 87 formed by the forward face of theprimary spool and the inner casing 29, the inlet valve body 30 andO-ring 78. The O-ring 78 forms a gas-tight seal so that the gas passesfrom annular channel 87 through the primary spool body at port 75 intoan annular chamber 83 formed by the primary spool body 62 and thesecondary spool body 79. The gas exits from chamber 83 through passage90 and port 92 into an annular exhaust ring or channel 94 which isconnected to the atmosphere by exhaust channel 95. At this time, theapparatus is ready to begin a repeat cycle of operation.

While the preferred embodiment of the invention has been disclosed, itis understood that the invention is not limited to such an embodimentsince it may be otherwise embodied in the scope of the appended claims.

What is claimed is:

1. A gas powered driving unit for converting gas pressure intorectilinear motion in a drive shaft, the unit comprising a main casing,a piston chamber having an abutment surface at one end thereof, pistonmeans including a drive shaft mounted for reciprocation in said pistonchamber, an inlet valve body mounted in said main casing adjacent saidpiston means, said inlet valve body defining a spool chamber and a valvechamber interconnected by a port, spool means slidably mounted in saidspool chamber, said spool means comprising a primary spool body and asecondary spool body, each said body being capable of independentmovement within said spool chamber, valve means mounted in said valvechamber, gas feed means leading to said valve means for the introductionof pressurized gas, said valve means being constructed to convey gasfrom said gas feed means into said spool chamber, said pri mary spoolbody being slidably mounted in said spool chamber and in one positionsealing against said valve means to effect the sealing of said valvemeans stopping gas conveyance of said valve means, means biasing saidprimary spool body into said one position trigger means for unseatingsaid primary spool body from said valve means and for enabling saidpressurized gas to initially thrust said primary spool body and thensaid secondary spool body in the direction of said piston means until incontact with said abutment surface, and for introducing said pressurizedgas to said piston chamber to thrust said piston means away from saidspool means, said primary and secondary spool bodies being togetherreturned by gas pressure into positions wherein said primary spool bodyseats against said valve means to intercept the passage of pressurizedgas therethrough, and exhaust means disenabled when said piston means isthrust away from said spool means by said pressurized gas, and enabledto exhaust the gas from said piston chamber, whereby said piston meansmoves towards said spool means.

2. A gas powered driving unit for converting gas pressure intorectilinear motion in a drive shaft, the unit comprising a main casing,piston means including a drive shaft reciprocally mounted in saidcasing, an inlet valve body mounted in said main casing, said inletvalve body defining a spool chamber and a valve chamber interconnectedby a port, spool means slidably mounted in said spool chamber, saidspool means comprising a moveable primary spool body and anindependently moveable secondary spool body, means biasing said pistonmeans against said primary spool body said primary spool body abuttingsaid secondary spool body to form a substantially ring shaped seat, afirst O-ring housed within said seat, said O-ring providing a gastightseal between the inlet valve body and said spool means and adapted tourge said primary spool away from said secondary spool when pressurefrom said piston means acting on said primary spool body is lessened,valve means mounted in said valve chamber, gas feed means connected tosaid valve means for the introduction of pressurized gas, said valvemeans being adapted to convey pressurized gas from said feed means intosaid spool chamber to move said spool means, said primary spool bodybeing slidably mounted in said spool chamber to assume a position inrepose seating against said valve means to effect the sealing of saidvalve means and stop the conveyance of gas by said valve means, triggermeans for unseating said primary spool body from said valve means, andfor enabling said pressurized gas to be conveyed into said spoolchamber, and exhaust means disenabled when said piston means is thrustaway from said spool means by said pressurized gas, and enabled forexhausting gas from said main casing, whereby said piston means movestowards said spool means.

3. A driving unit as claimed in claim 2 wherein the depth of thesubstantially ring shaped seat section formed by the primary spool bodyis less that the depth of the seat section formed by the secondary spoolbody.

4. A driving unit as claimed in claim 2, wherein said valve means has athroughgoing passage allowing gas to pass therethrough into said spoolchamber.

5. A driving unit as claimed in claim 2, wherein said inlet valve bodydefines a stepped spool chamber and the outer surface of the valve bodydefines a plurality of annular rings carved into the inlet valve bodywith feed means being provided in said inlet valve body to connect saidvalve chamber with a source of gas.

6. An inlet valve body as claimed in claim 5, wherein said inlet valvebody includes a filter chamber therein, said filter chamber beingconnected to said valve chamber by a passageway.

7. An inlet valve body as claimed in claim 5, wherein each of said spoolchamber steps has a different diameter, the larger step chamber sectionbeing of sufficient diameter to hold the primary spool and the otherstepped section being of sufficient diameter to hold at least a portionof the secondary spool body.

8. A driving unit as claimed in claim 2, wherein said primary spool bodyhas a forward head, said forward head being adapted to engage saidpiston means, with the other end terminating in a projecting tip, saidprojecting tip being adapted to engage said valve means to effect thesealing of gas passing through said valve means.

9. A primary spool body as claimed in claim 8, wherein said forwardheads outer edge forms a rib with a shoulder cut therein, saidshouldered rib forming a substantially ring shaped seat in cooperationwith the second spool to hold an O-ring, said shoulder cooperating withsaid secondary spool body to place said O-ring under compression so thatthe O-ring will expand toward the piston means forcing the primary spoolbody away from the secondary spool body when the compressive forces ofthe piston means are removed from the forward head of the primary spoolbody.

10. The primary spool body as claimed in claim 9, wherein a port is cutthrough the outer rib of said forward head.

11. A gas powered drive unit as claimed in claim 2, wherein saidsecondary spool body has a substantially annular body configuration witha bore out therethrough and a primary spool engaging rib projecting fromsaid annular body.

12. A secondary spool body as claimed in claim 11, wherein saidsecondary body rib has a shoulder cut therein, said shoulder beingadapted to engage against the primary spool body to form a seat for anO-ring.

13. A secondary spool body as claimed in claim 11, wherein one end ofsaid secondary spool body has a plurality of radial slots formedtherein.

14. A gas-powered driving unit for converting gas pressure intorectilinear motion in a drive shaft, the unit comprising a main casing,an inner casing mounted in said main casing, said inner casing defininga piston chamber, piston means slidably mounted in said piston chamber,said piston means comprising a drive shaft, a piston head connected tosaid drive shaft, said piston head having a ring out therein, an O-ringmounted in said ring, and spring means surrounding said drive shaft andbiasing said piston head, an inlet valve body mounted in said maincasing adjacent said inner casing, said inlet valve body defining aninterconnected stepped spool chamber and a valve chamber, a plurality ofchannels cut in the outer surface of said inlet valve body and gas feedmeans provided in said inlet valve body to connect said valve chamberwith a source of gas for the introduction of pressurized gas, spoolmeans slidably mounted in said spool chamber, said spool meanscomprising a moveable primary spool body and an independently moveablesecondary spool body mounted on said primary spool body, said primaryspool body comprising a forward head at one end adjacent said pistonmeans, with the other end terminating in a projecting tip and an annularrib projecting from said body, said secondary spool body having asubstantially annular configuration with a throughgoing bore, a ribprojecting from said annular body to engage said primary spool, saidengaging rib abutting said primary spool forward head to form asubstantially ring-shaped seat, a first O-ring mounted in said seat toprovide a gas tight seal between the inlet valve body and said spoolmeans, a second O-ring mounted around said primary spool body to providea gas tight seal between said primary spool body and said secondaryspool body, a third O-ring mounted around said secondary spool body toprovide a gas tight seal between said secondary spool body and saidinlet valve body, valve means mounted in said valve chamber for enablingthe passage of pressurized gas, said valve means being adapted to engagethe projecting tip of said primary spool body to seal gas conveyed bysaid valve means, trigger means to unseat the projecting tip of saidprimary spool body from said valve means, and gas exhaust means definedby said spool means and said inlet valve body.

1. A gas powered driving unit for converting gas pressure intorectilinear motion in a drive shaft, the unit comprising a main casing,a piston chamber having an abutment surface at one end thereof, pistonmeans including a drive shaft mounted for reciprocation in said pistonchamber, an inlet valve body mounted in said main casing adjacent saidpiston means, said inlet valve body defining a spool chamber and a valvechamber interconnected by a port, spool means slidably mounted in saidspool chamber, said spool means comprising a primary spool body and asecondary spool body, each said body being capable of independentmovement within said spool chamber, valve means mounted in said valvechamber, gas feed means leading to said valve means for the introductionof pressurized gas, said valve means being constructed to convey gasfrom said gas feed means into said spool chamber, said primary spoolbody being slidably mounted in said spool chamber and in one positionsealing against said valve means to effect the sealing of said valvemeans stopping gas conveyance of said valve means, means biasing saidprimary spool body into said one position trigger means for unseatingsaid primary spool body from said valve means and for enabling saidpressurized gas to initially thrust said primary spool body and thensaid secondary spool body in the direction of said piston means until incontact with said abutment surface, and for introducing said pressurizedgas to said piston chamber to thrust said piston means away from saidspool means, said primary and secondary spool bodies being togetherreturned by gas pressure into positions wherein said primary spool bodyseats against said valve means to intercept the passage of pressurizedgas therethrough, and exhaust means disenabled when said piston means isthrust away from said spool means by said pressurized gas, and enabledto exhaust the gas from said piston chamber, whereby said piston meansmoves towards said spool means.
 2. A gas powered driving unit forconverting gas pressure into rectilinear motion in a drive shaft, theunit comprising a main casing, piston means including a drive shaftreciprocally mounted in said casing, an inlet valve body mounted in saidmain casing, said inlet valve body defining a spool chamber and a valvechamber interconnected by a port, spool means slidably mounted in saidspool chamber, said spool means comprising a moveable primary spool bodyand an independently moveable secondary spool body, means biasing saidpiston means against said primary spool body said primary spool bodyabutting said secondary spool body to form a substantially ring shapedseat, a first O-ring housed within said seat, said O-ring providing agas-tight seal between the inlet valve body and said spool means andadapted to urge said primary spool away from said secondary spool whenpressure from said piston means acting on said primary spool body islessened, valve means mounted in said valve chamber, gas feed meansconnected to said valve means for the introduction of pressurized gas,said valve means being adapted to convey pressurized gas from said feedmeans into said spool chamber to move said spool means, said primaryspool body being slidably mounted in said spool chamber to assume aposition in repose seating against said valve means to effect thesealing of said valve means and stop the conveyance of gas by said valvemeans, trigger means for unseating said primary spool body from saidvalve means, and for enabling said pressurized gas to be conveyed intosaid spool chamber, and exhaust means disenabled when said piston meansis thrust away from said spool means by said pressurized gas, andenabled for exhausting gas from said main casing, whereby said pistonmeans moves towards said spool means.
 3. A driving unit as claimed inclaim 2 wherein the depth of the substantially ring shaped seat sectionformed by the primary spool body is less that the depth of the seatsection formed by the secondary spool body.
 4. A driving unit as claimedin claim 2, wherein said valve means has a throughgoing passage allowinggas to pass therethrough into said spool chamber.
 5. A driving unit asclaimed in claim 2, wherein said inlet valve body defines a steppedspool chamber and the outer surface of the valve body defines aplurality of annular rings carved into the inlet valve body with feedmeans being provided in said inlet valve body to connect said valvechamber with a source of gas.
 6. An inlet valve body as claimed in claim5, wherein said inlet valve body includes a filter chamber therein, saidfilter chamber being connected to said valve chamber by a passageway. 7.An inlet valve body as claimed in claim 5, wherein each of said spoolchamber steps has a different diameter, the larger step chamber sectionbeing of sufficient diameter to hold the primary spool and the otherstepped section being of sufficient diameter to hold at least a portionof the secondary spool body.
 8. A driving unit as claimed in claim 2,wherein said primary spool body has a forward head, said forward headbeing adapted to engage said piston means, with the other endterminating in a projecting tip, said projecting tip being adapted toengage said valve means to effect the sealing of gas passing throughsaid valve means.
 9. A primary spool body as claimed in claim 8, whereinsaid forward head''s outer edge forms a rib with a shoulder cut therein,said shouldered rib forming a substantially ring shaped seat incooperation with the second spool to hold an O-ring, said shouldercooperating with said secondary spool body to place said O-ring undercompression so that the O-ring will expand toward the piston meansforcing the primary spool body away from the secondary spool body whenthe compressive forces of the piston means are removed from the forwardhead of the primary spool body.
 10. The primary spool body as claimed inclaim 9, wherein a port is cut through the outer rib of said forwardhead.
 11. A gas powered drive unit as claimed in claim 2, wherein saidsecondary spool body has a substantially annular body configuration witha bore cut therethrough and a primary spool engaging rib projecting fromsaid annular body.
 12. A secondary spool body as claimed in claim 11,wherein said secondary body rib has a shoulder cut therein, saidshoulder being adapted to engage against the primary spool body to forma seat for an O-ring.
 13. A secondary spool body as claimed in claim 11,wherein one end of said secondary spool body has a plurality of radialslots formed therein.
 14. A gas-powered driving unit for converting gaspressure into rectilinear motion in a drive shaft, the unit comprising amain casing, an inner casing mounted in said main casing, said innercasing defining a piston chamber, piston means slidably mounted in saidpiston chamber, said piston means comprising a drive shaft, a pistonhead connected to said drive shaft, said piston head having a ring cuttherein, an O-ring mounted in said ring, and spring means surroundingsaid drive shaft and biasing said piston head, an inlet valve bodymounted in said main casing adjacent said inner casing, said inlet valvebody defining an interconnected stepped spool chamber and a valvechamber, a plurality of channels cut in the outer surface of said inletvalve body and gas feed means provided in said inlet valve body toconnect said valve chamber with a source of gas for the introduction ofpressurized gas, spool means slidably mounted in said spool chamber,said spool means comprising a moveable primary spool body and anindependently moveable secondary spool body mounted on said primaryspool body, said primary spool body comprising a forward head at one endadjacent said piston means, with the other end terminating in aprojecting tip and an annular rib projecting from said body, saidsecondary spool body having a substantially annular configuration with athroughgoing bore, a rib projecting from said annular body to engagesaid primary spool, said engaging rib abutting said primary spoolforward head to form a substantially ring-shaped seat, a first O-ringmounted in said seat to provide a gas tight seal between the inlet valvebody and said spool means, a second O-ring mounted around said primaryspool body to provide a gas tight seal between said primary spool bodyand said secondary spool body, a third O-ring mounted around saidsecondary spool body to provide a gas tight seal between said secondaryspool body and said inlet valve body, valve means mounted in said valvechamber for enabling the passage of pressurized gas, said valve meansbeing adapted to engage the projecting tip of said primary spool body toseal gas conveYed by said valve means, trigger means to unseat theprojecting tip of said primary spool body from said valve means, and gasexhaust means defined by said spool means and said inlet valve body.